Recent and ongoing innovations in fiber optic technology have resulted in the increased use of optical fibers in a number of applications, including optical communications. This increased use has led to a need for efficient peripheral devices that assist in the transmission of data through the optical fibers. One such peripheral device is an optical switch. An optical switch operates to selectively couple one optical fiber to a second optical fiber such that the coupled optical fibers are in communication with each other.
Two optical fibers in an optical switch can be coupled together with micro-machined tilting mirrors, or microelectromechanical system (MEMS) tilting mirrors, to direct a beam of light from an input optical fiber to an output optical fiber. The alignment of the tilting mirrors is critical to the performance of an optical switch. Each tilting mirror must be precisely aligned to receive a beam of light from, or transmit a beam of light into, a corresponding optical fiber. When one or more tilting mirrors are out of alignment, less light enters an output optical fiber resulting in losses in optical signal power.
FIG. 1 illustrates a simplified diagrammatic side view of an alignment system in an optical switch according to the prior art. Optical switch 100 includes a collection of input optical fibers 102, output optical fibers 104, input lenses 106, and output lenses 108. A fixed mirror 110 is positioned between and opposing two arrays of micro-machined tilting mirrors 112, 114. The alignment of optical switch 100 is maintained by transmitting an alignment beam of light 118 from a test light source 116 to a directional optical coupler 120. The coupler 120 injects the alignment beam 118 into a data information beam of light 122 propagating through optical switch 100. The two beams of light 118, 122 propagate through the optical switch and, upon exiting an output fiber 124, are received by a directional coupler 126.
Typically, the alignment beam of light 118 has a wavelength band different from that of the data information beam of light 122 in order to render the alignment beam 118 discernible from the data information beam 122. Accordingly, the directional coupler 126 directs the alignment beam of light 118 onto a detector 128, which generates a signal representative of the alignment beam of light 118. The detector 128 transmits the signal to a controller 130, which determines the accuracy of the alignment for the pair of tilting mirrors 132, 134. The controller 130 generates compensation signals that are fed back to actuators 136, 138 connected to tilting mirrors 132, 134 respectively, to cause actuators 136, 138 to adjust the tilt of the mirrors 132, 134 to minimize losses in signal power.
The alignment system of FIG. 1 requires a large total number of test light sources, directional optical couplers, and detectors to align the optical switch. A coupler is needed for each input and each output optical fiber in the switch, a detector is needed for each output fiber, and a test light source is needed for each input fiber. The alignment system of FIG. 1 also requires a considerable amount of time to align the switch, since individual pairs of tilting mirrors are adjusted independently.